Often, in the treatment of cancer through chemotherapy, different patient's tumors respond differently to different drugs. The ability to accurately predict the response of a specific patient to each of the drugs that might be used would greatly aid treatment.
The clonogenic assay, as described by Puck et al., J. Exp. Med., 103:653-666 (1956) and applied by Hamburger et al., Science, 197:461-463(1977), was developed in the late 1970s and became widely used for in vitro drug response assays for tumor cells. It is based on the ability of disaggregated tumor cells to grow in an agar or agar-like medium and form colonies. That assay correlates relatively well with clinical drug resistance but has several problems, such as the small percentage of tumors that can be evaluated, poor predictivity of clinical drug sensitivity and clump artifacts. Also, this technique requires a very long time to supply useful data and has difficulty in testing multiple drugs which detract from the usefulness of that assay.
Modifications of the clonogenic assay have been developed [for example the Kern and Weisenthal thymidine-incorporation clonogenic assay, Kern et al., J. Natl. Cancer Inst. 82:582-588 (1990) and the suspension-cell dye-incorporation assay, Weisenthal et al., Cancer Res., 43:258-264 (1983)]. However, these assays show a less than desirable prediction of clinical drug sensitivity and a low evaluation rate for solid tumors. In addition, all of these assays are artifactual in that they involve separating single cells from the original tissue.
Short term assays, such as are described by Sanflippo et al., Eur. Urol., 16:450-455 (1989), in which tumor fragments and tritiated nucleic acids are used, show some good clinical correlations but limit the viability of the tumors, which basically limits their use to the institution from which the tumors are derived.
Recently, as described by Vescio et al., Proc. Natl. Acad. Sci. USA, 84:5029-5033 (1987), an assay using a three-dimensional human-tumor sponge-gel-supported histoculture system with a [.sup.3 H]thymidine-incorporation endpoint has been developed, based on the earlier development of sponge-gel culture by Leighton as described in J. Natl. Cancer Inst., 12:545-561 (1951) and 15:275-293 (1954). This histoculture system allows tumor fragments to grow while maintaining many of their in vivo properties, including tissue architecture [Hoffman et al., Proc. Natl. Acad. Sci. USA, 86:2013-2017 (1989)]. Using histoculture with [.sup.3 H]thymidine incorporation measured by histological autoradiography, in vivo drug resistance can be accurately predicted. However, while in vivo drug response, or chemosensitivity, is accurately predicted for some drugs it is not for others.
Using the MTT end point as described by Ford et al., Cancer Chem. Pharmacol. 24:295-301 (1989) on cells in suspension, relatively high in vitro-in vivo correlations have been observed, Suto et al., J. Surg. Oncol., 42:28-32 (1989). The application of the MTT end point to the histoculture assay has been found (Furukawa et al., Int. J. Cancer, 51:489-498 (1992)) to increase the overall in vitro-in vivo correlative ability of the assay. However, formazan crystal formation from MTT due to succinate dehydrogenase activity is measured in this method by spectrophotometric methods after extraction, which does not allow simultaneous histological observation, does not correct for tumor heterogeneity and is labor intensive.
Thus, there is a continuing need for in vitro assays that accurately and rapidly predict in vivo drug response for a wide variety of drugs and permit observation of the variable drug response in a well maintained histoculture to take into account the heterogeneity present in the tumor with regard to drug response.